1. Field of the Invention
The present invention relates to a honeycomb structure. More particularly, it relates to a honeycomb structure capable of preventing the development of cracks generated in buffer portions and preventing the honeycomb structure from being divided when an operation (regeneration) of burning collected particulate matters is repeated.
2. Description of the Related Art
A honeycomb structure made of a ceramic material having excellent thermal resistance and corrosion resistance is employed as a carrier for a catalyst device or a filter which is used for environmental protection, the collection of a specific substance or the like in various fields of chemistry, power, steel and the like. Especially in recent years, the honeycomb structure has been a plugged honeycomb structure. Cell openings at both end surfaces of the structure are alternately plugged. The structure has often been used as a diesel particulate filter (DPF) which collects particulate matters (PM) discharged from a diesel engine or the like. Moreover, as a material of the honeycomb structure for use in the atmosphere of a corrosive gas at a high temperature, silicon carbide (SiC), cordierite, aluminum titanate (AT) or the like is preferably used, because the material has excellent thermal resistance and chemical stability.
Silicon carbide has a comparatively large coefficient of thermal expansion. Therefore, when a large honeycomb structure formed by using silicon carbide as an aggregate is used, a defect is generated owing to thermal shock sometimes. Moreover, the defect is generated owing to the thermal shock sometimes when the collected particulate matters are burnt and removed. In consequence, when the honeycomb structure having a predetermined size or more is manufactured by using silicon carbide as the aggregate, a plurality of small segments of the plugged honeycomb structure are usually prepared, and joined together to prepare a large joined article, and the outer periphery of the article is roughly processed and ground, to form the plugged honeycomb structure having a desired shape such as a cylindrical shape (see, e.g., JP-A-2003-291054). It is to be noted that the segments are joined together by using a joining material. The side surfaces (the outer peripheral surfaces) of predetermined segments are coated with the joining material, and the side surfaces of the segments are joined to one another.